Traps for catching crab, commonly referred to as "crab pots," are well known. Crab pots typically include a box-shaped chamber defined by a metal trap frame that supports walls of netting or wire. A piece of bait meat is suspended in the center of the chamber by a hook or canister. One or more entrance tunnels formed in the netting extend inwardly to terminate in a generally rectangular entrance frame. Each entrance frame defines a trap opening or "eye" through which a crab may pass when entering the chamber of the trap in search of the bait. Each eye is positioned above a floor of the trap so that crabs fall into the chamber and are prevented from escaping. The bottom portion of the tunnel netting is called the tunnel ramp. So that crabs may easily enter the trap, it is important that the tunnel ramp is pulled taut. To pull the tunnel ramp taut, structural lines connect the entrance frames to draw them together toward the center of the chamber. To maximize the vertical spacing between the chamber floor and the eye, the entrance frame may be oriented in an inclined position so that the eye faces generally upward toward a top wall of the trap. The increased vertical spacing enables more crabs to accumulate within the chamber before any are able to easily escape through one of the entrance openings. The trap is lowered from a fishing vessel to the sea floor where crabs are believed to be located. A buoy, attached to the top of the trap by a line, floats on the surface of the water to facilitate location of the trap for retrieval after the trap has been allowed to "soak" for a time sufficient for it to fill with crabs, typically a few days.
Traps of this type may also be used to catch other types of marine animals, especially bottom-dwelling fish such as cod and the like. When fishing for swimming species, the eyes of the trap must be fitted with one-way entrance gates that allow marine animals to enter the trap but not to exit. These entrance gates, called "triggers" in the industry, may also be used when fishing for crabs or other crawling species to prevent the trapped crabs from escaping by crawling on the walls to reach one of the entrance openings.
When fishing for cod or other swimming species, some fishermen prefer to have each entrance opening oriented in a generally vertical plane to provide a more direct path through the trigger to the trap's bait. Vertical orientation is particularly important for effective operation of triggers having an elongated or tunnel-like profile. The inclined entrance frames of a typical crab trap may be converted to a vertical "cod position" (and vice-versa) by rearranging the structural lines that suspend the entrance frames in position relative to the trap frame. When converting an inclined entrance frame to the vertical position, slack tunnel netting is gathered and tied to the entrance frame to keep both the tunnel and the eye taut. One drawback of converting an inclined entrance opening to the vertical position is that the entrance tunnel netting stretches unevenly with use, which causes undesirable sagging in the tunnel ramp when the entrance opening is converted back to the inclined position for crab fishing. Also, converting the entrance opening from the inclined position to the vertical position and back again requires substantial time and effort. Thus, there is a need for a trigger that is effective for cod fishing when used in the inclined position to alleviate the need to convert entrance openings between inclined and vertical positions.
U.S. Pat. No. 4,184,283 of Wyman and U.S. Pat. No. 5,168,653 of Wyman et al. describe prior-art crab-trap triggers comprising comb-like structures formed of resilient, plastic tines rigidly mounted at one end to the entrance frame of a trap. The free ends of the tines extend inwardly across the entrance opening so that crabs are allowed to enter the trap by flexing the tines. The tines are arranged so that a trapped marine animal attempting to exit the trap will depress the tines across the entrance opening to block the exit path. U.S. Pat. No. 4,843,756 of Wyman et al. describes a similar trigger having a rectangular frame supporting resilient plastic tines around the entire frame. The tines extend inwardly from the rectangular frame toward the chamber of the trap so that they converge at their free ends. The extension of the tines from the entrance frame makes this trigger best suited for use with a vertically oriented entrance frame. The bottom tines of this trigger can be held open by slow-moving starfish or other creeping species as they enter the trap, which can provide an opportunity for trapped fish and faster-moving marine animals to escape.
A consideration in the design of triggers is minimizing the resistance encountered by a marine animal entering the trap. A marine animal that encounters too much resistance upon attempting to pass through the entrance gate is likely to be deterred from entering the trap. The flexibility and durability of plastic tines is significantly affected by environmental conditions. The impact resistance of the plastic tines is reduced when they are exposed to the cold temperatures to which traps are typically subjected during use and during on-deck storage, making the triggers susceptible to breakage. In the off-season, traps are typically stored out-of-doors where the damaging effects of sunlight, ultraviolet radiation, and heat can cause the tines to deform and become brittle.
U.S. Pat. No. 4,905,405 of Hendricks describes a prior-art trigger that includes a metal frame supporting top and bottom sets of rotatably mounted, rigid plastic fingers. The top set of fingers is weighted, e.g., by a metal insert, and hinged downwardly from a journal rod that extends horizontally across the top portion of the entrance opening. The bottom set of fingers is rotatably connected to a second journal rod that extends horizontally across the bottom portion of the entrance opening. The bottom set of fingers is formed of a plastic material that is buoyant in water so that the fingers extend upwardly from the second journal rod. The top and bottom fingers are independently hinged to rotate inwardly in response to a marine animal entering the trap. The frame includes stop bars positioned generally parallel to the journal rods to prevent outward rotation of the fingers. The top and bottom sets of plastic fingers are staggered so that the free ends of the fingers alternate to block the egress of a trapped marine animal. The bottom fingers of this trigger can be held open by slow-moving starfish or other creeping species as they enter the trap, which can provide an opportunity for trapped fish and faster-moving marine animals to escape. The trigger is complex and expensive to manufacture.
Hendricks teaches that galvanic corrosion of metal parts that are exposed to salt water induces small electrical currents originating at the site of the corrosion, i.e., the surface of the corrodible metal parts. Because crabs and fish are sensitive to this electrochemical phenomena and will tend to avoid its source, corrodible metal trigger parts are undesirable.
Most commercial traps have rectangular entrance openings of a size that has become a de facto standard in the industry. However, traps having "non-standard" size entrance openings may require triggers of non-standard sizes, especially if the trigger includes both top and bottom mounted fingers. The trigger described by Hendricks is not easily adapted to fit non-standard sizes of entrance openings.
U.S. Pat. Nos. 5,478,273 of Ives and 5,771,627 of Mattson et al. describe crab pots specially designed for catching Dungeness crabs. Dungeness crabs are a particularly aggressive species of crab. These crab pots feature all-metal construction and permanently installed triggers to help contain Dungeness crabs once caught. The entrance frames include top and bottom rods spaced apart in a vertical plane. The triggers comprise pairs of spaced-apart wire fingers that are formed of a single length of wire looped around the top rod at two places to form a hinge. A span of the wire connects the loops near the top rod. The pairs of wire fingers hang from the top rod and across the entrance opening to rest against the bottom rod. Because the triggers are hinged directly to the entrance frame, they may not be removed for repair or replacement without bending or breaking the triggers or the entrance frame. Installation of this type of trigger on an existing, triggerless non-Dungeness crab trap would require the tunnel netting of the trap to be partially removed before the trigger wires could be wrapped around the entrance frame to form the hinge. Tools and significant time and effort would be required for its installation. When reinstalled, the tunnel netting would likely interfere with the operation of this type of trigger.